In Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems of a 3rd Generation Partnership Project (3GPP), a Transmission Time Interval (TTI) is a basic unit for scheduling downlink and uplink transmission in a time domain. For example, in an LTE/LTE-A Frequency Division Duplex (FDD) system, a time dimension is divided into radio frames having the length of 10 ms, herein each of the radio frames includes ten sub-frames and the length of the TTI is equal to the length of the sub-frame and is 1 ms. Each of the sub-frames includes two time slots and each time slot is 0.5 ms long. Each downlink time slot contains seven Orthogonal Frequency Division Multiplexing (OFDM) symbols (six OFDM symbols are included under an extended cyclic prefix), and each uplink time slot contains seven Single Carrier-Frequency Division Multiplexing Access (SC-FDMA) symbols (six SC-FDMA symbols are included under the extended cyclic prefix).
Compared with the LTE/LTE-A system, 3GPP subsequent evolution such as a 5th Generation (5G) mobile communication system will support a higher rate (Gbps), a massive link (1M/Km2), an ultra-low time delay (1 ms), higher reliability, hundredfold energy efficiency improvement and the like so as to support a new change in a demand. Among them, the ultra-low time delay as a key index in a 5G technology has a direct impact on the development of time delay constrained services such as an Internet of vehicles, industrial automation, remote control and an intelligent power grid.
However, an air interface time delay index of the existing LTE/LTE-A system is about 10 ms, which no longer meets the demand. An effective solution is to reduce the length of the TTI. For example, by reducing the 1 ms length of the TTI to 0.5 ms length or even 1-2 OFDM symbols, the minimum scheduling time may be reduced manyfold and thus the single transmission time delay is reduced manyfold.
When the length of the TTI is reduced, a transmission structure for sending an Acknowledgement (ACK) instruction, a Negative Acknowledgement (NACK) message and a Scheduling Request (SR) in an existing Physical Uplink Control Channel (PUCCH) will not be directly used. And meanwhile, with the reduction in the number of the symbols in the TTI, the overhead of Reference Symbols (RS) is too large. Therefore, there hasn't any appropriate technical solution yet at present.